Apparatuses of this sort are frequently also referred to as application heads, and are employed for example when foil or film-type substrates such as labels are to be coated extensively with liquid adhesive, for example hot-melt glue. Normally the flowable adhesive is kept in reserve in a fluid source such as a melting unit. This fluid source is connected to a basic body of the apparatus through a hose connection. Flowable adhesive is carried by a means of conveyance through corresponding holes into the apparatus and on through a distribution channel, and passes through a valve body of an applicator valve. The distribution channel communicates with a slit-shaped nozzle opening, from which the adhesive is dispensed and applied onto a substrate. Since the substrate is movable relative to the apparatus, adhesive is applied extensively to the substrate. Normally the nozzle opening is designed as an elongated slit. The length of the effective section of the slit can be adjusted by a piston that is movably situated in the distribution channel. Such an apparatus is known, for example, from DE 299 08 150.
When coating labels which are to be applied, for example, to bottles, the nozzle opening is normally in a vertical orientation; that is, the slit-shaped discharge opening runs essentially vertically. This can result in the occurrence of an unwanted downward flow component of the fluid in the longitudinal direction of the slit-shaped discharge opening, due to gravity. When the apparatus is stopped for an extended time, a subsequent dripping continues to be disadvantageously perceptible, due to the fact that surplus adhesive runs down the nozzle opening and in time hardens unchecked. In consequence, before each new start-up of the apparatus the adhesive that has run down must be laboriously removed in order to guarantee a uniform application pattern in the coming application.
In those uses in which the application pattern has a plurality of spaced apart strips, application apparatuses are regularly employed with a nozzle arrangement which uses nozzle plates that have a plurality of spaced cutouts, so that within the nozzle arrangement spaced, slit-shaped discharge openings occur through which the adhesive is dispensed in strips and applied to the substrate. To change the application width or pattern, the nozzle plate is uninstalled and a new nozzle plate with a different geometry is inserted into the nozzle arrangement. This process is relatively expensive and complicated. The same is true in the event that the application width must be changed.
The object of the present invention is to improve and to specify an apparatus in which influences of gravity on the flow in the slit-shaped nozzle opening are reduced. Furthermore, according to another aspect the object of the invention is to provide an apparatus that avoids disadvantageous influencing of the application pattern, in particular when the discharge opening is situated vertically, to minimize running down of the adhesive when the apparatus is stopped. According to another sub-aspect, the object is to specify an apparatus in which the shape of the discharge opening, in particular the width of the application pattern, can be modified as simply as possible.